Why do I keep seeing more flies on my farm?
Q:The fly situation on my small farm was terrible last year. I’m not sure if it was because of the weather conditions (we had a very wet spring) or the fact I have three horses now instead of two, but my seven acres seemed to be overrun with flies.
Also, I’ve heard about parasitic bugs that can kill fly larvae, reducing fly populations. Will these still work on small farms like mine or will they just fly off the farm to other locations? If I used them, when would I need to have the bugs on board to reduce the fly population? Do you have any other suggestions for how I can make next year less buggy?
A:Variations in weather patterns can affect fly development. Flies breed more slowly when it’s cold and faster when it’s warm. An ideal flybreeding habitat combines moisture and warm temperatures. When conditions are excessively wet it means that more material remains at ideal heat and moisture levels to increase the survival rate of developing flies, leading to a population boom. When conditions are excessively dry, there are fewer suitable breeding areas, so flies may migrate farther than normal in search of the right conditions.
Fly parasitoids may be a good control option for your property. These tiny, non-stinging, non-biting wasps kill manure-breeding flies in their pupal stage, preventing them from emerging as adults and laying eggs. How, where and when you disperse fly parasitoids can influence their effectiveness. We suggest customers give us a call so we
can get specific details about their situation, the layout of their land, and which species of flies are the problem---as many fly species have preferential breeding sites.
When shopping for fly parasitoids, be sure to ask about the species provided by the company. Spalding provides species information in its brochure; if you are dealing with a different commercial provider, you may need to ask for this information.
Once fly parasitoids are deployed on a property, they stay there. These are tiny insects that are poor fliers and will only travel about 150 feet in their whole lifetime. Fly parasitoids spend their time searching through substrates such as manure, bedding and decaying organic matter, looking for fly pupae ---which serve as both their food and a host to their offspring---thus killing flies by both predation and parasitism.
As for how well fly parasitoids will work for small farms, it really comes down to what the surrounding area is like. Most filth flies that bother horses have a range of about a quarter to a half mile, so if you’re considering fly parasitoids, I suggest that you drive around your area and take a look at your property on a satellite map (like Google Maps), and note anything within that range that may affect your fly populations.
A farm with three horses in a suburban or rural area with no other major fly-breeding sources would likely see a tremendous reduction in flies when fly parasitoids are used. On the other hand, a farm with three horses next door to a large boarding facility (say 50 horses) would probably not see a great deal of fly improvement with parasitoids, because most of the flies are breeding in areas outside of the owner’s control. In a situation like that, traps would probably be the best option. As for other suggestions, I do have a few:
• Be proactive, ask questions, and create an Integrated Pest Management (IPM) program for your property.
IPM programs work well, because they facilitate the use of multiple methods of control while minimizing pesticide exposure, to help avoid flies building resistance.
• Contact your local county extension agent. Extension agents are a great resource that tends to be underused. Generally, they are knowledgeable about many different types of pests or concerns particular to their county, and they can offer guidance and, sometimes, other resources as well.
• Do a little research on your own to better understand your situation.
The key is to focus on reliable sources of information. When looking up a particular type of pest using a search engine such as Google, focus on articles from major universities and avoid those posted in blogs or on pest-control websites. Information on a pest from a university website will offer up-to-date information on the pest as well as the best control methods.
Jessica Starcevich
Entomologist, Spalding Labs
Peoria, Illinois